Atherogenic autoantigen: oxidized LDL complexes with beta2-glycoprotein I

Lupus Anticoagulant and Anticardiolipin Antibody IgG are Associated with Increased Atherosclerosis at the Suprainguinal Elastic and Infrainguinal Muscular Arteries in the Abdomen and Lower Extremities

Purpose

Whether antiphospholipid antibodies (aPLs) cause atherosclerosis in certain arteries with specific compositions and locations remains unknown. We investigated the relationship between aPLs and their association with locations of atherosclerosis in the arteries of the abdomen and lower extremities.

Methods

Of 2273 patients, 697 who underwent computed tomography angiography of the abdomen and lower extremities and aPL evaluation were included. Atherosclerosis distribution score (ADS) was employed to quantify atherosclerosis severity. Multiple linear regression analysis was performed using the ADS of the suprainguinal elastic and infrainguinal muscular arteries as dependent variables and all aPLs, conventional risk factors of atherosclerosis, and coagulation-related factors as independent variables.

Results

In the suprainguinal elastic and infrainguinal muscular arteries, common risk factors for higher ADS were age, smoking, hypertension, higher glycated hemoglobin, male sex, decreased protein S, and increased homocysteine. Lupus anticoagulant (LA) and increased triglyceride level in the suprainguinal elastic arteries and anticardiolipin antibody (aCL) immunoglobulin (Ig)G, longer alcohol consumption duration, and increased fibrinogen level in the infrainguinal muscular arteries were also risk factors for higher ADS.

Conclusion

LA and aCL IgG were associated with atherosclerosis in the suprainguinal elastic and infrainguinal muscular arteries, respectively. aPLs could predict the location of atherosclerosis.

Immune mechanisms associated with cardiovascular disease in systemic lupus erythematosus: A path to potential biomarkers

Systemic lupus erythematosus (SLE) patients display an increased risk of cardiovascular disease (CVD). With the improved clinical management of other classical severe manifestation of the disease, CVD is becoming one of the most relevant complications of SLE, and it is an important factor causing morbidity and mortality. Several immune constituents have been shown to be involved in the pathogenesis of atherosclerosis and endothelial damage in SLE patients, including specific circulating cell populations, autoantibodies, and inflammatory mediators. In this review, we summarize the presentation of CVD in SLE and the role of the autoimmune responses present in SLE patients in the induction of atherogenesis, endothelial impairment and cardiac disease. Additionally, we discuss the utility of these immune mediators as early CVD biomarkers and targets for clinical intervention in SLE patients.

Understanding Accelerated Atherosclerosis in Systemic Lupus Erythematosus: Toward Better Treatment and Prevention

Systemic lupus erythematosus (SLE) carries a significant risk of cardiovascular disease (CVD). The prevalence of premature CVD is especially noteworthy because it occurs in premenopausal women with SLE who would otherwise have very low rates of CVD. While traditional risk factors likely play a role in development of CVD in the setting of SLE, they do not fully explain the excess risk. The pathogenesis of CVD in SLE is not fully understood, but the inflammatory nature of SLE is believed to be a key factor in accelerating atherosclerosis. Systemic inflammation may lead to an abnormal lipid profile with elevated triglycerides, total cholesterol, and low-density lipoprotein cholesterol and dysfunctional high-density lipoprotein cholesterol. Additionally, the inflammatory milieu of SLE plasma promotes endothelial dysfunction and vascular injury, early steps in the progression of atherosclerotic CVD. Despite the overall headway that has been achieved in treating lupus, innovative therapeutics specifically targeting the progression of atherosclerosis within the lupus population are currently lacking. However, there have been advancements in the development of promising modalities for diagnosis of subclinical atherosclerosis and detection of high CVD risk patients. Due to the significant impact of CVD on morbidity and mortality, research addressing prevention and treatment of CVD in SLE needs to be prioritized. This review explores the intricate interplay of SLE-specific properties that contribute to atherosclerosis and CVD within this population, as well as screening methods and possible therapies.

Soluble Vascular Biomarkers in Rheumatoid Arthritis and Ankylosing Spondylitis: Effects of 1-year Antitumor Necrosis Factor-α Therapy

OBJECTIVE

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) have been associated with cardiovascular disease. The treatment of arthritis by tumor necrosis factor-α (TNF-α) inhibitors may decrease the serum concentrations of vascular biomarkers. We determined circulating levels of oxidized low-density lipoprotein (oxLDL)/β₂ glycoprotein I (β₂-GPI) complexes, antibodies to 60 kDa heat shock protein (anti-Hsp60), soluble urokinase plasminogen activator receptor (suPAR), and B-type natriuretic peptide (BNP) fragment in sera of RA and AS patients undergoing anti-TNF treatment.

METHODS

Fifty-three patients with RA/AS were treated with etanercept or certolizumab pegol for 1 year. Circulating oxLDL/β₂-GPI complex (AtherOx), anti-Hsp60 IgG, and BNP8-29 fragment levels were assessed by ELISA. suPAR levels were determined by suPARnostic Quick Triage test. Flow-mediated vasodilation (FMD), carotid intima-media thickness (CIMT), and arterial pulse wave velocity (PWV) were determined by ultrasound.

RESULTS

One-year anti-TNF treatment significantly decreased oxLDL/β₂-GPI levels, as well as suPAR levels in patients with critically high suPAR levels at baseline. In RA, BNP levels were higher in seropositive vs seronegative patients. Serum levels of these vascular biomarkers variably correlated with lipids, anticitrullinated protein antibodies, rheumatoid factor, and C-reactive protein. CIMT positively correlated with BNP, and PWV with suPAR and anti-Hsp60, whereas FMD inversely associated with anti-Hsp60. In repeated measures ANOVA analysis, disease activity supported the effects of anti-TNF treatment on 12-month changes in oxLDL/β₂-GPI. CIMT supported the effects of therapy on changes in anti-Hsp60 and suPAR.

CONCLUSION

These biomarkers may be involved in the pathogenesis of atherosclerosis underlying RA/AS. TNF inhibition variably affects the serum levels of oxLDL/β₂-GPI, suPAR, and BNP.

Elevation of serum oxLDL/β2-GPI complexes was correlated with diabetic microvascular complications in Type 2 diabetes mellitus patients

BACKGROUND

High levels of oxLDL/β2-GPI complexes might be a consequence of LDL atherogenic modification mediated by oxidative stress. We aimed to determine whether the levels of serum oxLDL/β2-GPI complexes were correlated with diabetic microvascular complications in type 2 diabetes mellitus (T2DM) patients.

METHODS

Levels of oxLDL/β2-GPI complexes, oxLDL, routine lipid/lipoprotein parameters were measured in 100 healthy controls, 128 T2DM patients without any microvascular complications, and 172 T2DM patients with microvascular complications. Spearman's correlation, multivariable linear regression logistic regression analysis, and receiver operating characteristic (ROC) curve were performed.

RESULTS

Levels of serum oxLDL/β2-GPI complexes and oxLDL were significantly higher in T2DM patients with microvascular complications (oxLDL/β2-GPI complexes: 1.10 ± 0.18 U/mL; oxLDL: 48.12 ± 7.24 mmol/L) than those in T2DM patients without microvascular complications (oxLDL/β2-GPI complexes: 0.98 ± 0.16 U/mL; oxLDL: 41.45 ± 6.81 mmol/L) and controls (oxLDL/β2-GPI complexes: 0.79 ± 0.15 U/mL; oxLDL: 27.85 ± 5.32 mmol/L). Variables that remained significantly associated with oxLDL/β2-GPI complexes were oxLDL (β = 0.568, P < 0.001), TC (β = 0.312, P = 0.013) and microvascular complications (β = 0.205, P = 0.027), which accounted for 58.3% of the variation of the level of oxLDL/β2-GPI complexes in T2DM patients (R² = 0.583). Logistic regression analysis demonstrated that elevation of oxLDL/β2-GPI complexes (OR = 3.14, 95% CI: 1.04-9.46, P = 0.042) and oxLDL levels (OR = 3.02, 95% CI: 1.16-7.83, P = 0.023) were independently associated with occurrence of microvascular complications. Cutoff value of oxLDL/β2-GPI for the presence of microvascular complications was 1.05 U/mL, and AUC area of ROC curve was 0.783 (95%CI: 0.713-0.853), yielding a sensitivity of 86.8% and specificity of 64.9%.

CONCLUSIONS

Elevation of serum oxLDL/β2-GPI complexes was associated with microvascular complications in T2DM patients.

Elevated Levels of Serum β2-Glycoprotein I/Oxidized Low-Density Lipoprotein Complexes Are Associated with Cerebral Infarction in Patients with Type 2 Diabetes Mellitus

Background

To determine whether the levels of β2-glycoprotein I (β2-GPI)/oxidized low-density lipoprotein (oxLDL) complexes are correlated with cerebral infarction in patients with type 2 diabetes mellitus (T2DM).

Material/Methods

The levels of β2-GPI/oxLDL complexes, oxLDL, routine lipid/lipoprotein parameters, oxidative stress molecules, and inflammatory factors were measured in 78 healthy controls, 82 diabetics without cerebral infarction, and 79 diabetics with cerebral infarction. Correlation, multiple linear regression, and logistic regression analyses were performed.

Results

Serum β2-GPI/oxLDL complexes and oxLDL levels were significantly elevated in cerebral infarction in patients with T2DM (β2-GPI/oxLDL: 1.09±0.16 U/mL; oxLDL: 47.83±8.17 mmol/L) compared with T2DM without cerebral infarction (β2-GPI/oxLDL: 0.95±0.13 U/mL; oxLDL: 41.24±7.12 mmol/L) and healthy controls (β2-GPI/oxLDL: 0.81±0.12 U/mL; oxLDL: 27.97±4.57 mmol/L). The levels of β2-GPI/oxLDL complex in lacunar infarction (1.16±0.15 U/ml) were significantly higher than atherothrombotic infarction (1.07±0.19 U/ml) and cardioembolic infarction (1.00±0.23 U/ml). In all patients with T2DM, the β2-GPI/oxLDL levels were positively correlated with total cholesterol (r=0.474, p=0.001) and triglycerides (r=0.431, p=0.003). oxLDL levels were positively correlated with total cholesterol (r=0.445, p=0.002). The logistic regression analysis indicated that elevated β2-GPI/oxLDL and oxLDL levels were independently associated with diabetic cerebral infarction.

Conclusions

Elevated levels of serum β2-GPI/oxLDL complexes are associated with cerebral infarction in patients with T2DM, especially in those with lacunar infarction.

C‑reactive protein/oxidized low density lipoprotein/β2‑glycoprotein i complexes induce lipid accumulation and inflammatory reaction in macrophages via p38/mitogen‑activated protein kinase and nuclear factor‑κB signaling pathways

Oxidized low-density lipoprotein (oxLDL) can bind to β2-glycoprotein I (β2GPI) and C-reactive protein (CRP) to form stable complexes, which exert certain effects in diabetic cardiovascular disease. A previous study by our group has confirmed that the resulting complexes promote atherosclerosis in diabetic BALB/c mice. The present study was designed to investigate the effects and potential mechanisms of oxLDL complexes on lipid accumulation and inflammatory reactions in RAW264.7 macrophages cultured in a hyperglycemic environment. Cultured cells were divided into seven groups, which were treated with phosphate‑buffered saline (control), CRP, β2GPI, oxLDL, CRP/oxLDL, oxLDL/β2GPI or CRP/oxLDL/β2GPI. The results revealed the formation of foam cells in the oxLDL, CRP/oxLDL, oxLDL/β2GPI as well as CRP/oxLDL/β2GPI groups. Compared with oxLDL, the three complexes induced less lipid accumulation (P<0.05) through inhibiting the expression of CD36 mRNA and promoting the expression of and ABCG1 mRNA (P<0.05 vs. oxLDL). Furthermore, the levels of inflammatory factors interleukin (IL)‑1β, IL‑6 and tumor necrosis factor‑α were elevated in the CRP/oxLDL and CRP/oxLDL/β2GPI groups (P>0.05 vs. oxLDL), and obvious effects on p38/mitogen‑activated protein kinase and nuclear factor (NF)‑κB phosphorylation were also observed in these groups (P<0.05 vs. oxLDL). These results suggested that CRP/oxLDL/βG2P1 complexes may induce lipid accumulation and inflammation in macrophages via the p38/MAPK and NF‑κB signaling pathways. However, some differences were observed between the complexes, which may be attributed to the property of each constituent; therefore, further studies are required.

Increased serum levels of β₂-GPI-Lp(a) complexes and their association with premature atherosclerosis in patients with rheumatoid arthritis

BACKGROUND

Our recent study found the existence of complexes of β₂-glycoprotein I (β₂-GPI) with lipoprotein(a)[Lp(a)] in circulation and the complex concentrations were increased in sera of systemic lupus erythematosus patients. The concentration of β₂-GPI-Lp(a) and its relationship with premature atherosclerosis were evaluated in rheumatoid arthritis (RA) patients.

METHODS

Serum concentrations of β₂-GPI-Lp(a) were measured in 53 active RA patients and 40 healthy controls by a "sandwich" ELISA. β₂-GPI-ox-LDL, ox-Lp(a), ox-LDL and anti-β₂-GPI were also measured by ELISAs. In addition, inflammatory markers were examined.

RESULTS

Serum β₂-GPI-Lp(a) (1.12±0.25 U/ml vs. 0.87±0.19 U/ml, P<0.0001) and β₂-GPI-ox-LDL (1.01±0.20 U/ml vs. 0.80±0.08 U/ml, P<0.0001) concentrations in RA were both significantly higher than those of controls. Ox-Lp(a) (8.38±6.69 mg/l vs. 5.49±4.31 mg/l, P<0.05) and ox-LDL (0.68±0.65 mg/l vs. 0.37±0.13 mg/l, P=0.001) were also higher in RA than in controls. The area under the ROC curve (AUC) for β₂-GPI-Lp(a) (0.787) was larger than for ox-Lp(a) (0.731). AUC of β₂-GPI-ox-LDL (0.858) was also larger than for ox-LDL (0.785). β₂-GPI-Lp(a) and β₂-GPI-ox-LDL were positively correlated with ox-Lp(a), ox-LDL and CRP, respectively.

CONCLUSIONS

β₂-GPI-Lp(a) complex concentrations increased in active RA. Inflammation and oxidative stress in RA contribute to the increase of ox-Lp(a) and subsequently the formation of β₂-GPI-Lp(a).

Accelerated atherosclerosis, arterial thromboembolism, and preventive strategies in systemic lupus erythematosus

With improved disease survival, arterial thromboembolism has become an important cause of morbidity in patients with systemic lupus erythematosus (SLE). A number of conventional and non-conventional risk factors are associated with accelerated atherosclerosis. Regular surveillance and control of traditional risk factors is mandatory, and so is the appropriate use of the statins, anti-malarial agents, anti-platelet agents, and anti-coagulation for primary and secondary prevention of arterial thromboembolism in SLE patients. Judicious use of corticosteroids, calcineurin inhibitors, hormonal replacement therapy, and the cyclooxygenase 2 inhibitors is equally important.

OxLDL/beta2GPI complexes and autoantibodies in patients with systemic lupus erythematosus, systemic sclerosis, and antiphospholipid syndrome: pathogenic implications for vascular involvement

Oxidized low-density lipoprotein (oxLDL) interacts with beta2GPI, forming oxLDL/beta2GPI complexes. Autoimmune vascular inflammation (and oxidative stress) may promote the formation of these complexes. The coexistence of oxLDL/beta2GPI complexes with autoantibodies to these complexes suggests an active pro-atherogenic role in vascular thrombosis and atherosclerosis. Immunoglobulin G (IgG) anti-oxLDL/beta2GPI antibodies have been regarded as pro-atherogenic, whereas IgM antibodies are thought to be anti-atherogenic. For this study, oxLDL/beta2GPI complexes, IgG, and IgM anti-oxLDL/beta2GPI antibodies were measured using enzyme-linked immunosorbent assay (ELISA). Measurements were taken in two patient groups: (1) those with systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and rheumatoid arthritis (RA); and (2) those with primary and secondary antiphospholipid syndrome (APS). For oxLDL/beta2GPI complexes, SLE and SSc patients had the highest mean optical densities (ODs) (P <.001), followed by RA (P = .139) and healthy controls. IgG anti-oxLDL/beta2GPI antibody distribution followed the same pattern observed with oxLDL/beta2GPI complexes, SLE and SSc (P <.001), RA (P = .08), and controls. IgM antibodies showed a reverse pattern, with the highest mean OD in RA (P <.001), followed by SSc (P = .007) and SLE (P = 143). Both IgG and IgM anti-oxLDL/beta2GPI antibodies were significantly higher in secondary APS patients compared with SLE controls without APS. In addition, the highest mean OD and prevalence of IgG anti-oxLDL/beta2GPI antibodies were observed in APS patients with a history of arterial thrombosis. These results may reflect the widespread vascular involvement seen in SLE and SSc, in contrast to the relatively low vascular involvement in RA. In SLE and SSc, high serum levels and prevalence of circulating oxLDL/beta2GPI complexes and IgG anti-oxLDL/beta2GPI antibodies indicate significant vascular oxidative stress as well as a possible pathogenic role in autoimmune-mediated atherosclerosis.

Effects of malondialdehyde content in low density lipoproteins on platelet adhesion

Platelets play a key role in thrombotic vascular occlusion at the side of an atherosclerotic plaque. Malondialdehyde (MDA) derivatives are components of oxidized LDL. Recent studies suggest enhanced adhesion of platelets on oxidized LDL, but evidence of MDA-modified LDL contribution to enhanced platelet adhesion is missing. The aim of this study was to investigate platelet adhesion on LDLs with various content of MDA and to analyze its physiological relevance. LDLs were isolated by hydroxyapatite chromatography then analyzed. MDA, vitamin E and vitamin A content was estimated by HPLC methods and adhesion of platelets on modified LDLs was assessed. Both MDA and hypochlorite reactions induced an increase of both malondialdehyde content and negative charge in LDLs preparations. In LDLs of iron-overloaded patients both MDA content and negative charge was also significantly increased. The analysis of data showed that enhanced negative charge of LDLs had only negligible influence on platelet adhesion. The binding of platelets on LDL particles modified by MDA resulted in an S-shape curve and was substantially enhanced by high levels of MDA in LDL preparations. Malondialdehyde content both in hypochlorite modified LDLs and in LDLs of iron-overloaded patient matched the lower part of the binding curve. The platelet adhesion on circulating LDLs modified in in vivo conditions of oxidation stress in blood of iron-overloaded patients depends with considerable certainty preferably on non-MDA derived changes in derivatized LDLs. On the other hand, oxidized LDLs in atherosclerotic lesions can be much more extensively modified by MDA resulting in surfaces with enhanced affinity to adhering platelets. Such LDLs may be accessible to platelets, due to endothelial denudation or plaque rupture.

Predictive and protective autoimmunity in cardiovascular diseases: is vaccination therapy a reality?

The role of the immune system in modulating atherosclerosis has recently been well documented. Studies have revealed that cellular and humoral immunity plays crucial roles in atherogenic plaque formation. This includes macrophages, CD4+ T cells and dendritic cells as well as autoantigens such as oxidized low density lipoprotein (oxLDL), heat shock proteins and beta2-glycoprotein I. Given these recent advances, various modifications of the immune system in experimental models have been proposed as therapeutic strategies, with the potential of inhibiting atherosclerosis progression. These modifications are switching the immune system (CD4+ T cells) from Th1 towards a Th2 anti-inflammatory cytokine secretion, and the induction of protective antibodies both of which may be induced by specific vaccination. Recent identification of specific immunoreactive antigenic epitopes on modified LDL, their successful implementation for immunization and the induction of atheroprotection, supports the idea that active vaccination may emerge as a novel immuno-modulating atheroprotective strategy.

Oxidized Low-Density Lipoprotein/β2-Glycoprotein I Complexes and Autoantibodies in Patients with Type 2 Diabetes Mellitus

Diabetes mellitus (DM) is associated with a high incidence of atherosclerotic cardiovascular complications that result from chronic metabolic abnormalities such as hyperglycemia-induced oxidative stress. The oxidative-modification of low-density lipoproteins (oxLDL) and oxLDL/beta(2)-GPI complex formation have been reported in patients with autoimmune disorders. OxLDL/beta(2)-GPI complexes and autoantibodies to these complexes were measured by ELISA in serum samples from 50 type 2 DM patients and 50 age/sex-matched healthy controls. Mean OD for oxLDL/beta(2)-GPI complexes in DM was 0.099 +/- 0.065 with 50% of patients reacting above the assay cutoff (P < 0.001 vs. controls). Mean OD for controls was 0.037 +/- 0.015 with 2% positives. Thirty-six (72%) DM patients were taking cholesterol-lowering statins and had a significantly lower mean OD complex level (0.092 +/- 0.071, P = 0.05) compared to patients not taking statins (0.112 +/- 0.05). Mean OD for IgG anti-oxLDL/beta(2)-GPI antibodies in DM was 0.157 +/- 0.112, similar to the controls (0.146 +/- 0.098, P = 0.328). Increased serum levels of oxLDL/beta(2)-GPI complexes may be a consequence of oxidative stress and LDL modification in DM. Lower levels of oxLDL/beta(2)GPI complexes in DM patients taking statins are in agreement with the antioxidant and antithrombotic properties of these drugs. No significant IgG autoantibody production was observed in this group of DM patients. The interaction of oxLDL with beta(2)-GPI in circulation suggests the intriguing possibility that oxLDL/beta(2)-GPI complexes may also play a role in the development of atherosclerosis and/or cardiovascular complications in DM.

Influenza and atherosclerosis: vaccination for cardiovascular disease prevention

In both animal and human studies, strong prothrombotic and pro-inflammatory effects have been observed after influenza infection. Influenza is an important trigger for acute coronary syndromes, and it has been shown that in the US it may cause up to 90,000 deaths per year simply by triggering fatal myocardial infarctions. Multiple case-control and cohort studies have shown that the influenza vaccine has a marked protective effect against cardiovascular events, decreasing the incidence of these events by 20 - 70% in the settings of primary and secondary prevention. Although influenza vaccination is an extremely cost-effective method of cardiovascular protection and is recommended for all patients with cardiac diseases, it is largely underused in these patients. Therefore, increased efforts should be directed towards educating physicians and patients about the benefits of influenza vaccination in patients with coronary heart disease.

The antiphospholipid syndrome and atherosclerosis: clue to pathogenesis

Regulation of blood vessels is intrinsically tied to inflammatory signaling. Recent research suggests that chronic inflammation is associated with atherosclerosis risk. The antiphospholipid syndrome is a prototypic autoimmune disease. Disturbance of blood vessel homeostasis in this disorder may increase risk for atherosclerosis by mechanisms that are direct (through antibody targeting of blood vessel-regulating proteins) or indirect (via inflammatory mechanisms that have recently been implicated in autoantibody-mediated thrombosis).